Remaining oil saturation measurements for CO2-EOR pilot in Saudi Arabia

Abstract

Enhanced oil recovery by CO2 injection is an effective method for recovering additional oil beyond water flooding. In recent years CO2-EOR has garnered considerable attention from an environmental perspective as it is considered a green-house gas. Saudi Aramco is implementing its first CO2-EOR and sequestration pilot project in a slightly depleted part of a carbonate reservoir. An important aspect of the pilot testing is the measurements of remaining oil saturation (ROS) before and after the CO2 flooding. This paper discusses a number of methods and techniques for ROS quantification before CO2 injection in the ongoing CO2-EOR pilot project. The suite of tests provide pre-CO2 injection saturations. Similar tests are planned post-CO2 injection to determine the reduction in ROS after the pilot has been completed. Several methods have previously been used to determine ROS in oil reservoirs. In this study different logging technologies were utilized for quantification of ROS before CO2 injection to generate baseline data. The logging included resistivity and dielectric techniques. These techniques were also combined with physical formation fluid tester and sponge core analysis to determine ROS in the targeted carbonate reservoir. Finally the results are compared with a single well chemical tracer test which was conducted in the area. This paper presents the results from various methods and explores the effect of different parameters such as lithology, porosity, salinity and water saturation on ROS quantification. The results from near wellbore techniques are compared with data from sponge core as well as the single well chemical tracer test. Methodologies of raw data processing and their interrelations are shared. This paper provides new insights into how various logging tools and coring can be optimized in the future to increase the certainty of ROS measurements.